Today the FDA external advisory committee, called VRBPAC, met to discuss and vote on the safety and effectiveness of two COVID19 vaccines (Moderna and Pfizer) for under 5 year olds. Many of us parents have been waiting a long time for this! Ultimately, the committee unanimously voted to approve both vaccines.

Many parents have fantastic questions. I was in attendance at the FDA meeting; here are the presentation slides. Below I answer questions I’ve frequently received, using data presented at the FDA meeting as well as recent scientific studies.

Does my child actually need the vaccine?

Yes. There is a tremendous burden of disease in this age group. Thankfully the rate of severe disease is lower compared to adults, but this is an inherently flawed comparison because kids don’t die as often as adults. Since the beginning of the pandemic, 442 children aged 0-4 years old have died from COVID-19. If we compare to other vaccine preventable diseases among children, deaths due to COVID19 are highest. We cannot become numb to these deaths.

In terms of hospitalization, children, and specifically those under age 5, did not fare well during our first Omicron wave. According to the CDC, children under 5 had the highest rate of hospitalizations compared to other pediatric groups. Among children hospitalized, 1 in 4 ended up in the ICU.

The rate of COVID19 hospitalization was particularly high in October 2021-April 2022 compared to previous flu years and compared to COVID19 hospitalizations the prior year (October 2020-September 2021).

Severe disease is not the only outcome of SARS-CoV-2:

Long COVID19 does occur among kids, and vaccines reduce the burden of long COVID by 15-50%.
We parents know that masking and social distancing very young kids can be nearly impossible. The layers of protection we can employ are less than optimal.
We have frequent, unexpected disruptions in care and schooling of children that contribute to the daily burden of COVID. While not perfect, vaccines will help reduce infections and transmission, inching us closer to less family disruptions.

What if my child was recently infected with COVID19?

This is a great question. We are still trying to understand the durability and breadth of infection-induced protection, especially as Omicron continues to mutate. Very recent scientific evidence shows that 32% of children failed to make antibodies against SARS-CoV-2 after confirmed infection and had mediocre T-cell responses. This isn’t surprising. As I’ve written before, Omicron-induced immunity among unvaccinated people does not protect against other variants of concern. In addition, the quality of response (i.e., memory B-cells and T-cells) is relative to the severity of infection. If a child had a mild infection (which many do), then they likely had a lower viral dose and that secondary protection is less likely. This underscores the importance of vaccinating kids regardless of previous infection.

Vaccines clearly improve protection. I captured the grainy photo below during the FDA presentation today. The blue bar, which represents antibody concentrations after a Moderna shot, significantly increased after vaccination among those who were not infected and those who were previously infected.

Vaccine + infection is called “hybrid immunity” and more than 20 studies among adults have shown it works fantastically due to complementary and broad protection: vaccine immunity targets the spike protein, and infection-induced immunity targets the whole virus. This doesn’t mean you should purposefully get your child COVID19, but we need to recognize this as a viable path to protection.

What vaccines will be available?

This vaccine rollout is a bit different as, for the first time, two mRNA vaccines will be available at the same time. There are meaningful differences between the two vaccine formulas (see my previous post for details). There were also meaningful differences in the clinical trials. The dosage is different, and more importantly, the number of doses is different. This means the vaccines are not on the same playing field, and we need to be careful comparing side effects and efficacy.

Are the vaccines safe?

Yes. During the clinical trials, side effects were minimal:

For 6-23 month olds, irritability (65% Moderna vs. 44% Pfizer) and drowsiness (40% Moderna vs. 20% Pfizer) were most common.
For 2-5 year olds, pain at injection site were most common (60-70% Moderna vs. 27% Pfizer), followed by fatigue.

For Moderna, 1 in 4 experienced a fever. Side effects were more common after Dose 2. For Pfizer, 1 in 20 experienced a fever, and side effects for Dose 3 were similar to Dose 2. The higher rate of Moderna side effects is due to the higher dosage of RNA.

No myocarditis cases were reported in either clinical trial. This is great but expected news. The clinical trials were not nearly large enough to capture such a rare event. Data from 5-11 year olds show no myocarditis safety signal unlike 12+ year old boys. The leading hypothesis is that myocarditis among teenagers is caused by a combination of increased hormones and genetics. This is a hint that we may not see myocarditis as an issue for our very youngest kids, but data will be closely followed.

In the Moderna clinical trial, there was one case of febrile seizure and rash, which occurred six hours after the first dose. The child went to the emergency department and was released to go home a few hours later. She had a second seizure two weeks later. She stayed in the study and received the second dose without a seizure or fever.

In the Pfizer clinical trial, one potentially life-threatening adverse event occurred in an infant—coffee was spilled on them causing a thermal burn. Pfizer reported it to the FDA. This is an example of the rigor and comprehensiveness behind clinical trials.

Are the vaccines effective?

Yes. The FDA required Moderna and Pfizer to prove immunobridging. This is a process that compares antibodies among this youngest age group to another age group (in this case, 16-25 year olds) in which the efficacy of a vaccine is already established. We already know this vaccine works well; we just need to be sure the dosage works for kids.

Clinical trials found that antibody numbers were comparable to the older age group. In other words, the 2 doses of Moderna and 3 doses of Pfizer worked.

Pfizer and Moderna also reported efficacy against COVID19 disease. Remember that the two aren’t on the same playing field because of different doses:

Moderna reported 37-46% efficacy against disease for 2-5 year olds after 2 doses. And 31-51% for 6-23 month olds after 2 doses.
- Moderna has already started testing Dose 3 and will have results this summer. It is clear that this is, at least, a 3-dose series for everyone. A third dose will substantially improve effectiveness for these kiddos.
Pfizer reported 80.3% efficacy after 3 doses.
- Notice below that after Dose 2, efficacy was close to 0% for the youngest kids. This is incredibly surprising as this means kids are not protected until Dose 3. THIS was the data we were waiting for for such a long time—it explains why Pfizer delayed the 2-dose EUA this past winter. It wouldn’t have passed the test.

We have a hard choice. Which vaccine should my kids get?

You cannot make a wrong decision. Either vaccine is better than nothing, and both help with severe disease and death.

To me, though, the choice is clear. My girls will get Moderna for four reasons:

The confidence in Pfizer’s efficacy is not strong… at all. Efficacy was only based on 3 cases in the vaccine group and 7 cases in the control group. Pfizer didn’t meet the standard protocol of 21 cases. This means the “true” effectiveness is unstable—it could be anywhere between 14% and 81%. We don’t know exactly where. Take 81% with a grain of salt.
Antibodies with Moderna reach the same levels in half the time compared to Pfizer (6 vs. 13 weeks). Kids are not protected until Dose 3 of Pfizer, which is a while.
Moderna confirmed they already started testing Dose 3 (booster) and will have data by this summer. We know that this vaccine is at least a 3-dose series. So, once we get Moderna and Pfizer on the same playing field, efficacy will be comparable. Importantly, Moderna is testing an Omicron-specific booster, not the original vaccine. This is different from the Pfizer trial, in which Dose 3 is the original formula. This is huge. By the end of summer, Moderna kids will likely be on the same playing field as adults, who will likely get a bivalent vaccine this fall.
FDA said they do not know whether the primary series for Pfizer is 3 doses or if this third dose is considered a booster. In other words, it may very well be that Pfizer kids will need a fourth dose for primary efficacy.

I was vaccinated and am currently breastfeeding. Should we delay the vaccine for my baby?

No, do not delay. Antibodies are transferred through breastmilk. In general, breastfeeding is reliably very helpful against GI infections (which will help with COVID), but it’s less clear whether it helps against respiratory infections. B-cells and T-cells are in breast milk too, but their role is complicated. We don’t think B-cells and T-cells in breast milk are helpful in a clinically meaningful way. Get your baby the vaccine.

I was vaccinated while pregnant. Can we delay vaccination to the child?

Vaccination while pregnant is different from protection conferred through breastmilk. Mothers pass antibodies through the placenta that enter the fetus’s circulation. It is clear that this is protective against respiratory viruses once the baby is born. These antibodies do wane quickly, though. (There are optimal periods for vaccination during pregnancy. If you want to maximize antibody transfer, you should get the vaccine during the third trimester.) Just like with breast milk, B-cells and T-cells are transferred to the womb, but their role is complicated, and we don’t think they are helpful in a clinically meaningful way. Get your baby the vaccine.

Should I wait for the larger dose if my child is turning 5 soon?

Do not wait. There was a key Moderna slide presented at the FDA meeting today which compared neutralizing antibodies (our first line of defense) across age groups, and thus compared dosages. The high level of neutralizing antibodies for 2-5 year olds (with the smaller dose) were comparable to children aged 6-11 years (with the larger dose). Moderna did test the larger dose (50 mcg) among 2-5 year olds in Phase I of the clinical trial but did not proceed because of high rates of fevers.

What’s next?

VRBPAC was the second stop in a long process to get the vaccine authorized for emergency use. FDA doesn’t have to listen to their advisory committee, but there’s no reason they would not. The data is clear. This Friday and Saturday the ACIP will meet, and quickly thereafter, the CDC will approve. This means vaccines could be in arms by next week.

Remember to sign up for V-safe!!

When you get your child vaccinated, remember to sign up for V-safe! This is an incredibly important CDC program, which allows us to understand the “real world” safety of vaccines for everyone, including our little ones. Sign up HERE.

Bottom line

This vaccine is safe and effective, and our littlest kids need it. Next week, I will be standing in line to finally get my girls protection from this now vaccine-preventable disease. I hope you will get your kids protected as well, as the evidence is clear.

Love, YLE

I have no conflicts of interest to report with either of these vaccine manufacturers.

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“Your Local Epidemiologist (YLE)” is written by Dr. Katelyn Jetelina, MPH PhD—an epidemiologist, biostatistician, wife, and mom of two little girls. During the day she works at a nonpartisan health policy think tank, and at night she writes this newsletter. Her main goal is to “translate” the ever-evolving public health science so that people will be well equipped to make evidence-based decisions. This newsletter is free thanks to the generous support of fellow YLE community members. To support the effort, please subscribe here:

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FDA meeting for <5 COVID vaccine: Q&A